ELI5: How does the body turn calories into energy? is it the stomach that does all the work?

Submitted by IsItInyet-idk t3_z7eb7x in explainlikeimfive

I read a story once about a guy who puts a treadmill in the basement and imagines as he works out and loses weight the little workers in his body have less work to do.

It's a horror so they end up getting mad and going after him .. but I kinda like the mental image to lose weight. So I tried to imagine my own little story line about the energy foreman in my body as I work to lose weight ...

But it turns out that while I understand the general gist.. im not sure HOW the body turns calories into energy. I know the digestion process removes nutrients to absorb.. but how does that turn into energy?

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tmahfan117 t1_iy64n34 wrote

Through a process called cellular respiration.

All your stomach does is break food down into simple parts, simple sugar, protein, and fat molecules.

Those parts then enter your blood and are pushed around your body and absorbed out of the blood into the cells that need them.

Sugars are your cells main energy source, and they break those sugars down into CO2 and H2O through Cellular Respiration to get energy for the cell.

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Moskau50 t1_iy656e1 wrote

Your mouth chews the food to physically break it down into smaller pieces. These go to the stomach, which uses acid to chemically break down the food into tiny molecules, making a sort of acid-nutrient soup. Your intestines neutralize the acid and begin absorbing the molecules from the "soup." The nutrients go into the blood stream, where they are provided to cells all over your body. Each cell makes its own energy through respiration; it can take a molecule of glucose (simple sugar) and break it down, step by step, into carbon dioxide and water, using some oxygen gas along the way. As it does so, it captures the energy by using those reactions to "energize" certain specific molecules; the cell is able to use these "energized" molecules to "power" other functions.

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vance_mason t1_iy6hlrr wrote

So the workers in the mine that is your stomach break up the food you just ate into 3 basic components: fats, proteins, and carbs. It then drops onto a conveyor belt (your intestines). As it rolls along the conveyor belt, it gets sorted out and pushed off the line into the appropriate department.

Carbs get taken to a lab, where they're further broken apart by workers to the basic building block: glucose. Now's where it gets fun. Depending on how much energy you need at a given moment, the workers either load the glucose into a machine (glycolysis cycle) or send it to your liver to be built into blocks called glycogen that it stores for later.

That Glycolysis machine has multiple steps, where it adds or removes things on the glucose until it becomes the final product, Pyruvate, which goes into 1 of 2 machines (depending if you have oxygen) aerobic or anaerobic. It's kind of like those Rube Golberg machines, where the marbles roll along, knocking things over and driving other steps? Along the way by products are being made, which get brought over to the mighty powerhouse of the cell, the Mitochondria. These byproducts are loaded in, and again drive a domino effect, which turns a wheel that generates the energy of your body: Adenosine TriPhosphate- ATP.

Fat and protein can both also be converted through various methods to become pyruvate and join in this cycle if there's not enough carbs. But that's the best 5 year old version I can give.

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